No, one is not a priest forever. You forget that God is the one who ordains a priest. You have no powers of a priest if you bind sin into your church.
Yes, I know there are plenty of "priests", or ministers etc. that bind sin into their church. People just don't realize that these "priests" have no power from God to intercede on his behalf. They are wasting their time being in that church.
That's why Christ warned us to be wary of them, Know them by their fruits.
Read on repentance by Ambrose. http://www.newadvent.org/fathers/
You, of course, are entitled to your own view of the matter but I simply articulated the orthodox catholic understanding of the Sacrament of Ordination as it has been understood for nearly two millenia.